Large quantities of oxygen are being increasingly required for use in partial oxidation processes such as those employed in the conversion of coal to liquid or gaseous products and those employed in the conversion of other solid fuels or refuse to useful products. Often an integrated gas turbine system is employed for the production of oxygen for use in these conversion processes. In an integrated gas turbine system, air is extracted from the compressor of the gas turbine system and is fed to a cryogenic air separation plant operating at elevated pressures. Some of the oxygen produced by the air separation plant may serve as oxidant for the gas turbine while most of the oxygen passes to the conversion process. Some of the fuel produced by the conversion process is passed to the gas turbine system as the fuel for the system.
Conversion processes such as are described above require not only very large quantities of oxygen but also oxygen at elevated pressure. Thus, especially in the case when an integrated gas turbine process is employed for the oxygen production, the air separation plant is operated at elevated pressures. Because of the decreased nitrogen to oxygen relative volatility which characterizes elevated pressure air separation plant operation, the recovery of oxygen from the air separation plant decreases with increased operating pressures. It is thus desirable to have a cryogenic separation system which can produce oxygen at elevated pressure and with high recovery.
Accordingly it is an object of this invention to provide a cryogenic rectification method which can produce oxygen at high recovery especially at elevated pressure.
It is another object of this invention to provide a cryogenic rectification apparatus which can produce oxygen at high recovery especially at elevated pressure.